John answered this one about a week ago:
Same basic reason I gave for the reason why the models have been struggling as of late with the details to the storms. We have had a split-flow type of setup going on across N. America. Not as classic as we typically see, but the jetstream that has the arctic air to the north of it this time of the year has been pretty reluctant to dip into the lower 48. Clipper systems like to dive in on that jet that divides the cold air from the really cold air.
Thus the mild start to the winter and also the absence of clipper type systems and LES.
-John
